There exist coordinate input apparatuses which are used to input coordinates to an input surface by using a pointer or finger to control a connected computer or write characters or graphics.
Conventionally, as coordinate input apparatuses of this type, touch panels of various methods have been proposed or become commercially available. These coordinate input apparatuses are widely used because a terminal such as a personal computer can easily be operated on the screen without using any special tool.
There are various coordinate input methods using, e.g., a resistive film or an ultrasonic wave. A method using light is also known, as described in U.S. Pat. No. 4,507,557. In this method, a retroreflecting sheet is arranged outside the coordinate input region. By illumination units which are arranged at the corners of the coordinate input region to illuminate an object with light and light-receiving units which receive light, the angles between the light-receiving units and a shielding object such as a finger that shields light in the coordinate input region are calculated. On the basis of the detection result, the pointing position of the shielding object is determined.
Japanese Patent Laid-Open No. 2000-105671 or 2001-142642 discloses an apparatus in which a retroreflecting member is arranged near the coordinate input region, and the coordinates of a point where retroreflected light is shielded are detected.
In, e.g., the apparatus described in Japanese Patent Laid-Open No. 2000-105671, the peak of a light-shielded portion by a shielding object, which is received by the light-receiving unit, is detected by waveform processing such as differential. With this processing, the angle of the light-shielded portion with respect to the light-receiving unit is detected, and the coordinates of the shielding object are calculated from the detection result. In Japanese Patent Laid-Open No. 2001-142642, comparison with a specific level pattern is done to detect one end and the other end of a light-shielded part and the center of the coordinates is detected.
In U.S. Pat. No. 4,507,557, pixels of a RAM imager serving as a light-receiving unit are read out and compared by a comparator to detect a light-shielded portion. If a light-shielded portion having a predetermined width or more is present, the center (½ position) of the pixels at the two ends is detected. On the basis of the detection result, the coordinates of the shielding object are calculated.
In the above-described method (retroreflective light shielded portion detection method) of detecting a light-shielded portion by a light-shielding object, however, the light beam to be shielded has a predetermined width that almost equals the width of the retroreflecting member in a direction perpendicular to the coordinate input surface. This poses no serious problem for switch input by a finger or the like. However, when a user is to input a character locus by using a pointer, the detection timing of pen-down operation at the start of input and that of pen-up operation at the end of input are delayed.
To solve this problem, a pen point switch means which executes a switch operation sensitively upon contacting the input surface may be arranged at the tip portion of a pointer such that the pen-up and pen-down timings are detected on the basis of a pen point switch signal obtained from the pen point switch means. However, when this structure is implemented, pen-down by a tool except the pointer, e.g., input by a finger is impossible.
Concerning this point, Japanese Patent Laid-Open No. 9-114592 discloses an arrangement including a switching means so as to implement a function of combining pen input (input of pen-up and pen-down signals) by a pointer and mouse input. In this case, however, the switching means is necessary, and this makes the operability poor.
In Japanese Patent No. 2986234, relative coordinate display and absolute coordinate display are switched in accordance with the coordinate input region. However, this arrangement cannot solve the problem of operability by the pen-up/pen-down detection timing in the retroreflective light shielded portion detection method.
Japanese Patent Laid-Open No. 2001-117685 discloses an arrangement which switches the mode by determining the inside or outside of a window region. However, this is switching between a handwriting input mode and a mouse input mode and not switching of the pen-up/pen-down detection timing. Hence, an improvement of operability in the retroreflective light shielded portion detection method cannot be expected.